Antibodies to phospholipids have been implicated in a variety of diseases or clinical conditions including arterial and venous thrombosis, recurrent fetal loss, thrombocytopenia, pulmonary embolism, coronary thrombosis, cerebral thrombosis, livedo reticularis and HIV infection.
It is therefore important to have a convenient and reproducible clinical method for detecting and measuring antiphospholipid antibodies in samples from patients.
A variety of phospholipids can give rise to antibodies in humans and antibodies specific to cardiolipin, phosphatidylinositol, phosphatidylserine and phosphatidylethanolamine, for example, have been found.
Not all of these antibodies are necessarily present in every disease associated with antiphospholipid antibodies. It is therefore desirable to be able to determine easily antibodies to various specific phospholipids.
Furthermore, antibodies to a particular phospholipid may be IgG, IgM or IgA type immunoglobulins and not all types may be present in all conditions; for example, IgA antibodies have been linked to adrenal insufficiency (Al-Momen et al., (1991), Thromb. Res., Vol 64, p. 571) and high levels of IgG antiphospholipid antibodies have been noted in systemic lupus erythematosus (Quamar, T. et al., (1990), Arthritis Rheum, Vol 33, p. 501).
It is therefore desirable to be able to distinguish antibodies of several immunoglobulin classes.
Presently available commercial methods for determining antiphospholipid antibodies are based on enzyme-linked immunosorbent assays (ELISA). Commercially available kits use cardiolipin as substrate and therefore detect only anti-cardiolipin antibodies.
Radioimmunoassays have also been used to measure anti-phospholipid antibodies but these have all the drawbacks associated with the use of radioactive materials.
A flow cytometric assay has also been reported for determining anti-cardiolipin antibodies (Pirruccello et al; (1990), J. Clin. Lab. Anal., vol. 4, p. 236). This assay utilises liposomes as carriers of the phospholipids. The difficulty of controlling liposome size makes standardization of the liposomes a problem. In addition, liposomes are generally composed of more than one phospholipid to lend stability to the liposome.
The methods presently available for determination of antiphospholipid antibodies are limited in their flexibility and convenience, particularly when one considers the increasing clinical need for determination of antibodies of different immunoglobulin classes and specific to particular phospholipids.